1. Field of the Invention
The present invention relates to electrophotographic apparatus and more particularly to such apparatus having improved means for coupling the conductive layer of photoconductive films or webs to a reference potential.
2. Description of the Prior Art
In electrophotography the use of photoconductive imaging elements in the form of films or webs has become increasingly popular, both in applications where the imaging element is intended for repeated use and in applications where the element is intended for a single use. Such elements usually comprise a photoconductor layer overlying a conductive layer on a support, e.g., a plastic film; and in most imaging procedures it is desired that the conductive layer, which is sandwiched between the other element layers, be coupled to a source of reference potential, usually ground potential.
A wide variety of techniques have been employed to provide such an electrical reference potential to the element's conductive layer (which procedure will hereinafter be referred to generally as "grounding"). In one approach special edge constructions, e.g., perforations, inbibed conductive coatings and abraded outer layer portions, have been formed to cooperate with specially designed contacting mechanisms in the electrophotographic apparatus. In other approaches sophisticated systems such as opposing corona chargers or molten alloy or mercury contact baths have been utilized.
Each of the above approaches is effective in a controlled environment; however, some suffer in reliability when not carefully controlled, and all involve fairly substantial additional cost increments to the imaging system. This additional cost is not so significant in more sophisticated apparatus which use the imaging element repeatedly; however, for less complex apparatus of the type in which the element has a single use, the cost is a significant disadvantage. Apparatus of this latter type often use supplies of the image element in roll form, and a common technique for grounding the film or webs is via the core on which they are wound. That is, the end portion of the roll is designed, in some fashion, to have electrical contact with the core and the core is grounded. Besides requiring special fabrication procedures, this approach also can produce potential differentials in the conductive layer, due to the long path (of the connection to the outer winds of the roll) and the significant resistance of the conducting layers.